1. Field of the Invention
The present invention relates to coherent detection, and more specifically, it relates to embodiments of the optical hybrid for use in coherent detection.
2. Description of Related Art
The optical hybrid is a device that is used for coherent signal demodulation for either homodyne or heterodyne detection. A 90° optical hybrid is a six-port device that mixes the incoming signal with the four quadratural states associated with the reference signal in the complex-field space. The optical hybrid would then deliver the four light signals to two pairs of balanced detectors.
The existing technologies for making optical hybrids are the waveguide approach, fiber coupler technology and micro-optics technology. The waveguide and the fiber approach require temperature control to hold the relative phase shift among the output ports. In addition to that, the cost is high. The micro-optics approach can make the device passive; however, the manufacturing process is more complex; it is therefore suitable only for high-end applications.